The present invention relates to a battery charging unit for an electrical or electronic device, particularly, although not exclusively, for a cellular radio telephone.
Commonly, portable cellular radio telephones are provided with removable batteries as their current source. Typically, these batteries are Nickel--Cadmium (Ni--Cd) batteries which are rechargeable.
To recharge the battery, the battery is left attached to the cellular radio telephone, and is recharged "in situ" by means of a charging unit. The charging unit is coupled to a mains alternating current (AC) supply via a conventional plug arrangement (in the United Kingdom, this is a 3-pin arrangement well known to persons skilled in the art), and is coupled to the battery via a multi-conductor cable to the telephone and through internal circuitry, to the battery to be recharged. Respective matching contacts are provided, on the casing of the telephone and in a plug terminating the free end of the cable, to couple current to the telephone and battery. The charger, typically, may be a simple transformer/constant current generator or switch mode power supply, as is well known to persons skilled in the art. The telephone may be provided with control logic and means to sense one or more parameters, for example battery temperature, these being indicative of the charge state of the battery. By monitoring such parameters, one is able to ensure that the battery is optimally recharged. With this method of recharging, the battery is "fast-charged", that is where a constant current of, for example, 600-1000 mA is supplied to the battery to effect recharging. The telephone can still be used whilst the battery is being recharged.
A problem with storing these chargers is that the cable becomes entangled with other objects and is difficult to store. The user usually has to somehow wrap the cable--usually around the main body of the charging unit which can make it bulky. Commonly, during storage, this cable comes unwrapped and tangled, which can be fiddly and time consuming to untangle.
Among the many accessories available for portable cellular radio telephones, are so-called "travel chargers". These take the form of a charging unit incorporating a transformer/constant current generator, with a pin arrangement for coupling it to the mains supply. The casing for the charging unit is provided with a recess for receiving a spare battery. Contacts are provided within the recess for contacting matching contacts on the battery. A "trickle" current is supplied to the battery when the charging unit is coupled to the mains supply, thereby slow charging the battery received therein. The charging unit does not incorporate control logic for controlling fast charging, and therefore, is only capable of slow-charging a spare battery. This takes some time. There is the problem, therefore, that should the battery currently being used as the power supply for the telephone become discharged before the spare battery is recharged, then the telephone is out of operation. Unfortunately, when the recess may be perfectly located when using a wall mounted socket, should a floor mounted socket or any type of horizontally arranged socket be used, the recess may then be at such an angle that the battery will not stay in the recess or, if it does, does not make contact with the contacts properly, making charging impossible.